1. Field of the Invention
The present invention is relates to a technique for evaluating electric characteristics of a device. This US patent application is based on Japanese Patent application Nos. 2007-099090 and 2008-065625. The disclosure thereof is incorporated herein by reference.
2. Description of Related Art
In order to evaluate the electric characteristics of a device, a method of making probes contact pads to measure a resistance between wiring lines is carried out. At this time, a contact resistance of the probe influences the measurement resistance. With influence of the probe contact resistance on an automatic measuring apparatus, even if an unnecessary resistance is added to the probe in the form of contamination to shift the electric characteristics a little bit, the measurement value falls within a manufacturing deviation and any problem is not caused.
However, recently, it is required to reduce the deviation with the finer processing. Accordingly, it is impossible to meet the measurement requisition only by an open/short check and a rough check of resistance between pads.
In an LSI with a high performance, recently, a sort process using not voltage but current is performed in the sort process in which a test of a MOSFET for characteristic monitor provided onto a product wafer is carried out. In this sort process, the sort is performed based on a threshold voltage Vth of the MOSFET but an ON current of the MOSFET. The threshold voltage sort is performed by measuring a small current in the order of microampere but the ON current sort is performed by measuring a current in the order of milliampere which is relatively large. Therefore, when a contact resistance of about 10Ω is attached to the probe, a voltage drop due to the contact resistance cannot be ignored, because the current reduces at a considerable rate. Thus, the sort is influenced based on the contact resistance. Also, in order to meet the strict sort rule, the measurement deviation cannot be ignored. Therefore, it is necessary to always keep the contact resistance of the probe to a low resistance. Ideally, the contact resistance of each probe must be kept to be equal to or less than 1Ω. Thus, a technique of measuring the contact resistance of the probe is demanded. Especially, the technique that can measure contact resistances of n (n≧3) probes is demanded.
In conjunction with the above description, a method of measuring a contact resistance of a probe is described in Japanese Patent Application Publication (JP-P2004-85377A: first related art). In this measuring method, a plurality of electrode pads connected with a wiring line is provided for a semiconductor device for an electric test to be carried out about. In this method of measuring a contact resistance, a current is supplied to the probe and a voltage is measured. Thus, the contact resistances of the whole probes are determined from the supplied currents and the measured voltages. Also, in a technique described in this first related art, it is not possible to measure the contact resistance of each probe precisely.
Japanese Patent Application Publication (JP-P2001-343426A: second related art) discloses a method of testing a semiconductor device. In this method, an impedance in a current path between two pads to which two probes are made contact is measured, and when the measured value is larger than a predetermined value, the probe is cleaned. However, in this method, the contact resistances of all the probes are not measured and cannot be determined.
Also, Japanese Patent Application Publication (JP-A-Heisei 8-82657: third related art) discloses a method of testing an integrated circuit device. In this method, a contact state of probes with a first pad section and a second pad section is detected. The first pad section is composed of a plurality of electrodes and the second pad section is composed of a plurality of electrodes having different resistances. In this technique, a resistance between two pads, a contact state and needle pressure can be detected, but the contact resistance of each probe cannot be determined precisely.
Also, Japanese Patent Application Publication (JP-A-Heisei 11-39898: fourth related art) discloses a semiconductor device. In this technique, a contact state of a probe group can be checked but the contact resistance of each probe cannot be determined precisely.
Also, Japanese Patent Application Publication (JP-P2004-119774A: fifth related art) discloses a semiconductor device. In this technique, a signal is given from a switching element so as to supply a voltage to an external connection pad. At this time, a contact check result to a pad is outputted based on a voltage appearing on a monitor pad.
Also, Japanese Patent Application Publication (JP-P2006-59895A: sixth related art) discloses a method of checking a conduciveness of a contact plug or via-plug. Many checking pads are arranged and the check is performed by using these pads.